Modern mobile devices continue to demand an increasing amount of operating time from a single battery charge. Accordingly, power management is a primary concern for many mobile device manufacturers. One major source of power consumption within a mobile device is the power amplifier used in the transmission of wireless signals. A well designed power amplifier may reduce the power requirements of the mobile device in which it is incorporated, thereby significantly extending the battery life of the mobile device.
During a mobile phone calibration, the input power of the power amplifier is swept to a power level as high as ˜10 dBm and to a maximum supply voltage of ˜4.5 V. Recently, however, envelope trackers have been integrated into the mobile phones. Most, if not all, envelope trackers have a boost mode that can raise the maximum power amplifier supply voltage to ˜5.5 V. This combination of high drive level and power supply voltage can result in a peak output power 3-4 dB above the normal operating conditions. This puts the power amplifier at risk of being damaged, and more recently, puts any surface acoustic wave (SAW) or bulk acoustic wave (BAW) duplex filters at risk of being damaged because these filters are being aggressively reduced in size, which limits their maximum safe power dissipation. It would be beneficial to limit power for power amplifiers during this mobile phone calibration stage, especially for those power amplifiers having envelope trackers, in order to avoid damaging SAW or BAW filters at the output of the power amplifier.
The present disclosure describes a differential power amplifier having a differential interstage power limiter that is most effective under these unique operating conditions to limit excess output power.